1. Field of the Invention
The invention relates to an optical sheet, particularly to a reflective sheet.
2. Description of the Related Art
FIG. 1 shows a schematic diagram illustrating a conventional reflective sheet. Referring to FIG. 1, the reflective sheet 100 is made from foamed polyethylene terephthalate (PET) 102, so multiple flat and densely spread bubbles 104 are formed in the reflective sheet 100. When light beams enter the reflective sheet 100, the light beams are additionally reflected by the interface between the bubbles 104 and the polyethylene terephthalate 102 to increase the overall reflectance of the reflective sheet 100. FIG. 2 shows a schematic diagram illustrating another conventional reflective sheet. Referring to FIG. 2, the reflective sheet 200 is made from polyethylene terephthalate (PET) 202 with reflective particles 204. The reflective particles 204 may be made from titanium dioxide (TiO2) or barium sulfate (BaSO4). When light beams enter the reflective sheet 200, the light beams are additionally reflected by the reflective particles 204 to increase the overall reflectance of the reflective sheet 200.
However, the conventional reflective sheets 100 and 200 are made from expensive polyethylene terephthalate and are each formed as a single-layer structure, and the single-layer structure is liable to warp or waving when brought to a standstill or heated to affect the optical performance. Hence, a material with high mechanical strength is selected for the reflective sheet to avoid the wrap or waving of the reflective sheet. However, the material with high mechanical strength is naturally hard. When a light guide plate 300 shown in FIG. 3A is stacked on the convention reflective sheet 100 or reflective sheet 200 to form a backlight module, light-scattering dots 302 formed on the light guide plate 300 and made from printed ink are liable to be injured or peeled off due to the squeeze given by the hard reflective sheet 100 or reflective sheet 200, as shown in an enlarged diagram of FIG. 3B, and dot patterns are also liable to be transferred to the reflective sheet 100 or the reflective sheet 200.